/Engine/Plugins/Animation/RigLogic/Source/RigLogicLib/Public/dna/layers/GeometryWriter.h
The joint indices must be stored in the same order as the weights they are associated with.
void setSkinWeightsJointIndices ( std::uint16_t meshIndex, std::uint32_t vertexIndex, const std::uint16_t * jointIndices, std::uint16_t count )